1. Field of the Invention
The present invention relates to machinery, and more particularly, to a motor having a structure capable of reducing generation of a magnetic resistance between a rotor and a stator, a method for manufacturing the motor, and a washing machine using the motor.
2. Discussion of the Related Art
Generally, a motor is a device for changing electrical energy to dynamic energy, and in particular, a device for generating dynamic energy using an electromagnetic force generated when current flows through a conducting wire arranged in an area where a magnetic field is generated.
Such a motor is widely used in machinery requiring motive power. Typically, such a motor is used in washing machines, refrigerators, and other appliances. The following description will be given in conjunction with an example of a drum washing machine using a motor.
Drum washing machines are classified into an indirect connection type in which a drive force from a motor is indirectly transmitted to a drum via a belt wound between a motor pulley and a drum pulley, and a direct connection type in which the rotor of a motor is directly connected to a drum such that a drive force from the motor is directly transmitted to the drum.
In the indirect connection or transmission type, energy loss occurs during power transmission carried out via the motor pulley and drum pulley. Furthermore, it is noisy. For this reason, the use of direct connection type drum washing machines using a brushless DC (BLDC) motor is increasing, in order to solve the above-mentioned problems incurred in direct connection type drum washing machines.
Hereinafter, the structure of a conventional direct connection type drum washing machine will be described in brief with reference to FIG. 1.
FIG. 1 is a vertical sectional view illustrating a configuration of a conventional drum washing machine. As shown in FIG. 1, the drum washing machine includes a cabinet 1, and a tub 2 installed within the cabinet 1. A drum 3 is centrally arranged in the tub 2 such that the drum 3 is rotatable.
A motor is mounted to the tub 2 at the rear of the tub 2. In detail, a stator 60 is fixed to a rear wall of the tub 2. A rotor 5 surrounds the stator 60 while being axially coupled with the drum 3 by a shaft 4 extending through the tub 2.
A door 7 is arranged at the front of the cabinet 1, to open or close the cabinet 1. A gasket 8 is interposed between the door 7 and the tub 2.
A hanging spring 9 is mounted between an inner top surface of the cabinet 1 and an upper portion of the outer circumferential surface of the tub 2, to support the tub 2. A friction damper 10 is also mounted between an inner bottom surface of the cabinet 1 and a lower portion of the outer circumferential surface of the tub 2, to attenuate vibrations generated at the tub 2 during a spin-drying operation.
Meanwhile, as shown in FIG. 2, the stator 60 includes a core 61 constituting a central portion of the stator 60, teeth 63 protruding from the core 61, and coils 65 wound around the teeth 63.
A space S is formed between the adjacent teeth 63, in order to allow the task of winding the coils 65 to be easily carried out. However, this space S reduces the effective torque of the motor.
Specifically, due to the space S, the magnetic resistance generated between the stator 60 and the rotor 5 is increased, thereby causing an increase in cogging torque and an increase in torque ripple. As a result, the effective torque of the motor is reduced, thereby causing a degradation in the performance of the motor. Cogging torque is a torque caused by a variation in magnetic resistance occurring in spaces due to a relative position variation between the rotor and the stator. Since such a cogging torque is not rendered to be an effective motor torque component, it is desired to reduce the cogging torque.
When increases in cogging torque and torque ripple occurs, there is a problem in that the generation of vibrations and noise in the motor is also increased.
In order to eliminate the problems caused by the space S, a proposal has been made, wherein each tooth has a trapezoidal tip 63a. In this case, however, there is a problem of material costs increasing in that the amount of scrap produced in the manufacture of the stator core is increased due to the trapezoidal cross-sectional shape of the tooth tips 63a. 